I'd read that a small percentage of sound that passes to the subwoofer is voice, and transitioning voice from front to back can be distracting. I already find it distracting when TV shows transition voice from side to front, but that is of course full voice, not the rare really low bits. But the Axiom guy and Audyssey apparently don't buy that "should be up front" argument. When I did the crawl, I wish I had also moved the sub to the secondary seating, to see if I could find a good position for both spots. Doing it again, I hope to get better info, now that it's not entirely new to me.
A couple more reasons for not putting it that direction to begin with was I thought it would do better if it hit a wall in 15' instead of 26'. Actually, it carries the 26' just fine, but it likely is why it hits a near-null on the secondary seats. Also, it's a crowded corner area with side speaker, floor lamp, recumbent bike, between fireplace and patio slider, with no place to go. I can't move the bike out into the room without messing up alignment for the primary TV chair. TV/speaker position is constrained by a 55 gallon fish tank. I was also concerned that stronger vibrations would kill the fish, and we've had them over 17 years. Moving TV over fireplace would solve the space problem, but everyone else objected.
Sub is about 4" from wall adjacent to the TV wall, about 20" away from component cabinet, 8" from a chair on the other side, which is right up against the fireplace hearth. Uneven spacing due to air vent. The fireplace mass may make it behave more like a corner. The sweet spot was 20" from the back corner, along the same fireplace wall. I didn't want the sub facing the long 26' direction (open to kitchen) instead of to the wall 15' away, thought it might affect the wave pattern, but next time I'll know more what to look for. It's really interesting where the sound goes, it carries well to the wall 26' away, I hear it better in the kitchen than on the sofa in the family room.